The normal motion of the foot in gait involves the periods of: (1) heel contact; (2) forefoot loading; (3) middle of midstance; (4) propulsion period; and (5) swing. During the period of heel contact it is necessary for the foot to absorb a significant shock and thereafter pronate to assume a firm contact with the running surface. The primary shock absorption occurs at the knee with a significant force being experienced in the calcaneous region of the heel.
Pronation of the foot is necessary to reduce shock as the weight is placed on the fatty pad of the calcaneous. The foot is dependent upon the subtalar joint, a universal type of joint connecting with the leg, to allow for transverse plane rotation by either eversion or inversion of the calcaneous, i.e. bending out or bending in of the leg after heel contact. Such contact pronation dampens the shock of the heel strike by the locking and unlocking of the foot joints. Pronation occurs from heel strike to full forefoot loading. Thereafter to propulsion supination occurs. The lifting of the lateral side of the foot acts to straighten out the force curve through the foot so that the final propulsion occurs through the hallux or the first metatarsal of the foot. Pronation of the foot is also responsible for proper flexing of the knee. Because the tibia must rotate faster than the femur in order to flex the knee, pronation must occur at a proper rate first for proper knee flexing.
Thus it can be seen that during running there is an initial heel shock which must be absorbed in the calcaneous region with ground contact. During running, and especially on uneven terrain or during turning, the foot is not always set down on a surface extending perpendicular to the leg thereby requiring pronation for accommodation with the running surface. Subsequent pronation is necessary for proper flexing of the knee. In each instance, however, the heel may receive the shock from a slightly different angle than through a force vector directly in line with the leg. In addition the fatty tissue beneath the calcaneous bears the brunt of the initial shock during heel contact and can present significant physical problems with sustained running exercises.
It is the purpose of the present invention to provide an orthotic stabilizer for incorporation in an athletic shoe to cushion the heel and prevent injury and to stabilize the foot during pronation.